bug(poller): pollComments exhausts Worker subrequest budget on dipper_ai

[liplus-lin-lay]

observation

Cloudflare Workers logs (2026-04-26 cron run) show `pollComments` failing with subrequest exhaustion specifically on Liplus-Project/dipper_ai:

```
pollComments: failed to fetch comments for Liplus-Project/dipper_ai#50: Too many subrequests by single Worker invocation
pollComments: failed to fetch review comments for Liplus-Project/dipper_ai#56: Too many subrequests
pollComments: failed to fetch reviews for Liplus-Project/dipper_ai#56: Too many subrequests
pollComments: failed to fetch comments for Liplus-Project/dipper_ai#56: Too many subrequests
pollComments: failed to fetch review comments for Liplus-Project/dipper_ai#10: Too many subrequests
pollComments: failed to fetch reviews for Liplus-Project/dipper_ai#10: Too many subrequests
```

Other 4 repos (github-rag-mcp / github-webhook-mcp / liplus-language / liplus-desktop) do not show the error.

hypothesis

dipper_ai has more comment-bearing issues/PRs than other repos, so the per-cron `pollComments` fan-out exceeds the 1000-subrequest-per-invocation budget. Same root cause as #130 (wiki side), different surface.

Existing caps in `pollComments`:

• `MAX_COMMENT_BACKFILL_PARENTS = 20` — limits parents per repo
• `MAX_COMMENTS_EMBEDDED_PER_REPO = 30` — limits embeddings

But each parent fetches 3 separate endpoints (comments + reviews + review_comments) before checking the embed cap. With many high-comment parents, fetch fan-out alone exceeds budget.

fix direction (memo)

Apply the same pattern as #130 / PR #131 (wiki):

• Cap total fetches per repo per invocation (parents-probed cap distinct from embeddings cap)
• Or: stagger comments-fetch across multiple cron runs (similar to diff backfill window)
• Or: per-parent budget cap that aborts mid-parent if subrequest counter overflows

related

• hotfix: wiki ingestion exhausts Worker subrequest budget on initial bulk poll #130 / PR hotfix(poller): cap wiki ingestion subrequest fan-out (#130, patch) #131 (wiki side, same root cause pattern)
• feat: index GitHub Wiki content into RAG (W4) #128 / PR feat: index GitHub Wiki content into RAG (W4, patch) #129 (W4 wiki, surfaced the budget issue first)

[liplus-lin-lay]

PR #144 (cap=30→10 incremental fix) merged. 2026-04-27 の PR #136 で auto-close されていたが、2026-04-28T15:15 UTC の本番観測で cap=30 でも Too many subrequests が解消していないことを確認したため、追加修正の検証期間として再 open する。次の :15 cron 1-2 周で fetch_failures=0 を確認後に close 予定。

[liplus-lin-lay]

PR #144 (cap=30→10) merge から 9 日経過、2026-05-07 10:48 JST に Cloudflare Workers Observability で本番観測：

• pollComments 直近 :15 cron 周 (10:15-10:16 JST): 5 リポすべて fetch budget reached for ... (10 fetches) warn のみ、fetch_failures=0 確認。
• failed to fetch 直近 1h: 0 events。

本 issue の close 条件 (fetch_failures=0 を :15 cron 1-2 周で確認後 close) は満たされたので close する。

なお Too many subrequests を 24h 範囲で見ると 90 errors を観測したが、内容は pollComments ではなく pollDocs / pollReleases 系 (Failed to poll docs/releases for {repo})。本 issue とは別 surface の subrequest exhaustion なので、別 issue で起票して扱う。